An Unusually Rapid Protein Backbone Modification Stabilizes the Essential Bacterial Enzyme MurA

Proteins are subject to spontaneous rearrangements of their backbones. Most prominently, asparagine and aspartate residues isomerize to their β-linked isomer, isoaspartate (isoAsp), on time scales ranging from days to centuries. Such modifications are typically considered “molecular wear-and-tear”,...

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Published inBiochemistry (Easton) Vol. 59; no. 39; pp. 3683 - 3695
Main Authors Zhang, Tianze, Hansen, Kjetil, Politis, Argyris, Müller, Manuel M
Format Journal Article
LanguageEnglish
Published United States American Chemical Society 06.10.2020
Subjects
Alkyl and Aryl Transferases - chemistry
asparagine
aspartic acid
bacterial enzymes
Bacterial Proteins - chemistry
Enterobacter cloacae - chemistry
Enterobacter cloacae - enzymology
Enzyme Stability
Isoaspartic Acid - chemistry
Isomerism
isomers
mass spectrometry
Models, Molecular
mutants
Protein Aggregates
Protein Conformation
Protein Folding
protein unfolding
proteins
site-directed mutagenesis
stoichiometry
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Summary:Proteins are subject to spontaneous rearrangements of their backbones. Most prominently, asparagine and aspartate residues isomerize to their β-linked isomer, isoaspartate (isoAsp), on time scales ranging from days to centuries. Such modifications are typically considered “molecular wear-and-tear”, destroying protein function. However, the observation that some proteins, including the essential bacterial enzyme MurA, harbor stoichiometric amounts of isoAsp suggests that this modification can confer advantageous properties. Here, we demonstrate that nature exploits an isoAsp residue within a hairpin to stabilize MurA. We found that isoAsp formation in MurA is unusually rapid and critically dependent on folding status. Moreover, perturbation of the isoAsp-containing hairpin via site-directed mutagenesis causes aggregation of MurA variants. Structural mass spectrometry revealed that this effect is caused by local protein unfolding in MurA mutants. Our findings demonstrate that MurA evolved to “mature” via a spontaneous post-translational incorporation of a β-amino acid, which raises the possibility that isoAsp-containing hairpins may serve as a structural motif of biological importance.
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ISSN:0006-2960
1520-4995
1520-4995
DOI:10.1021/acs.biochem.0c00502